Field of the Technology
The present disclosure generally relates to equipment and techniques for centrifugal casting. The present disclosure more specifically relates to equipment and techniques for centrifugal casting of metallic materials.
Description of the Background of the Technology
Metallic casting generally includes supplying a volume of molten metallic material to a static or rotating mold and allowing the material to cool to produce a casting shaped by the mold. Castings may be cast in near net form or may be further modified in subsequent forging or machining applications to produce final components. Metallic materials shrink during phase transition from liquid to solid, which may result in castings comprising uncontrolled shrinkage porosity, especially in difficult to cast metallic materials such as, for example, titanium aluminide (TiAl) based alloys and other TiAl materials. Shrinkage porosity is inherent to the fundamental solidification mechanics and may negatively impact microstructure as well as casting yield. In general, minimized internalized porosity may be addressed by processing techniques such as hot isostatic pressing (HIP). However, uncontrolled internal porosity may result in surface distortions affecting surface quality of the casting and increase production costs. Uncontrolled internal porosity may also be exposed when castings are sectioned or separated from casting components. When porosity is surface connected, current processing techniques may be unsuitable for many casting applications. For example, surface treatment techniques designed to fill or enclose porosity may fail to maintain the continuity of the casting, which may detrimentally affect mechanical properties of the cast material. Material removal techniques such as machining to remove external porosity may also reduce casting yield and expose additional porosity.
Conventional casting techniques for casting various metallic materials, such as titanium aluminide based alloys, are incapable of controlling porosity such that the porosity is internalized away from both the surface of a casting and regions of the casting that may be subsequently sectioned. For example, others have described preparation of titanium aluminide sections using a series of static casting and vacuum arc remelting techniques. These static casting techniques, however, create significant porosity, which cannot be removed using HIP. Others have also described centrifugal casting techniques for preparation of titanium aluminide castings that require supplying molten material to the centrifuge before the centrifuge reaches rotational speed. Cooling rate and solidification, however, are difficult to control, as is evident by the requirement of a separate heating method and mold for each cast piece. Although various other centrifugal casting techniques have been reported, none are able to adequately control shrinkage porosity.
Given the drawbacks associated with conventional casting techniques for casting metallic materials, including centrifugal casting techniques, it would be advantageous to develop improved techniques for casting metallic materials.